Vehicle manufacturers outfit their vehicles with an increasing number of wireless communications capabilities. Telematics units installed in modern vehicles can wirelessly communicate both voice and data communications between the vehicle and a variety of recipients, such as a central facility, over a wireless carrier network. The increased number of vehicles and other devices that can wirelessly communicate has created a corresponding increase in the number of communications, such as short-message service (SMS) messages. Given the increased number of communications, at least some messages from these sources may be unwanted by a recipient. And when protecting against spoofing or other attacks it can be challenging to determine which SMS messages have been sent from trusted senders and which messages have not.